It can be difficult to tell males and females apart because their adult plumage is identical and their characteristics are similar. The call is different between the male and female and this is the primary and most reliable way of telling hens from cocks in Guinea fowls.
Male Guineas make a one syllable sound when alerted by anything unusual, a loud and repetitive - ChI-Chi-Chi-chi noise. The adult female is called the Guinea hen She makes a commonly - buck-wheat,buck-wheat. It is made more difficult by the fact she can imitate the sound of the cock.
Below: A male guinea fowl:
You can see his wattles are large, red and cup shaped.
The male’s helmet and wattles tend to be larger than the females and the males wattles are more whilst the females is more blue. The wattles are cupped in the cockerel and flat in the hen. But the easiest way to distinguish them is by their calls.
Below: A female guinea fowl.
Notice the smaller wattles with more blue then red and flatter in shape.
Sexing keets is not impossible, I have bought sexed keets from a bird supplier in the past. It is beyond the average backyard keeper to vent sex young guineas.
Other ways to sex Guinea Fowl :This should read not sexing guinea fowl, it is practically impossible before 10 weeks of age and difficult even after that.
They are sexed by their call, the males have a single tone screech and they females have a two tone call.
The males do start developing a little earlier and have a slightly redder face and thicker/bigger wattles. Next to quietening guineas, the hardest problem can be to sex them.
Male and female guinea fowls differ so little in appearance that many find it difficult to distinguish them from each other. Usually, sex may be distinguished by the cry of the birds after they are about 2 months old and by larger helmet and wattles and coarser head of the male. In young male guineas aged 12 to 15 weeks, the wattles are larger, curve out more and have thicker edges than the females.
By 15-16 weeks the females wattles are also thickening. The adult male has a slightly larger helmet and wattles and coarser head than females. The cry of the female sounds like a buckwheat, buck-wheat or put-rock, put-rock, and is quite different from the one-syllable shriek of the male. When excited, both the male and female emit one-syllable cries, but at no time does male's cry sound like buckwheat, buckwheat.
Adult guineas do make more noise than chickens and will create a ruckus if disturbed, they prefer to walk or run and are fully paid up members of the ministry of silly walks. They tend to fly only when frightened, excited or roosting.
The wattles size, shape and colour is a General Rule of Thumb and not always accurate. Relying on the female's two-syllable call is the best and earliest way of telling who's what.
There are some proposed Guinea Fowl Standards and according to these, male Guinea Fowl should have large cupped wattles that stick out from the face, female Guinea Fowl should have smaller wattles that lay flat to the face.
The adult guinea male is called a cock. He is also recognised by having larger wattles than the female, and a somewhat larger helmet.
As keets determining the sex is nearly impossible, until they discover their voices at about 8 weeks of age. The size of the wattles on keets will be the nearly the same until they are a few months old when the wattles of the male begin to develop. (Vent sexing keets is difficult.)
Although wattle size and some actions may suggest the sex of a adult guinea fowl, sound is the sure way to determine the sex (as is vent sexing older guineas).